Ceramic foam filter

Abstract

The present invention resides in an improved ceramic foam filter particulary useful for filtering molten metal. The composition of the ceramic foam material is as follows: 50 to 70% Al 2 O 3 ; 2 to 10% micron sized reactive alumina; 1 to 5% montmorillonite; 1 to 10% ceramic fibers; and from 5 to 25% of a ceramic binder or air setting agent.

What is claimed is: 
     
       1. A ceramic foam filter for use in filtering molten metal having an open cell structure characterized by a plurality of interconnected voids surrounded by a web of ceramic, said foam consisting essentially of the following composition: 55 to 70% Al 2  O 3 , 2 to 10% micron-sized reactive alumina, 1 to 5% montmorillonite and 1 to 10% ceramic fibers wherein said micron-sized reactive alumina acts in synergism with said montmorillonite to achieve a homogeneously distributed bonding phase and a suitable slurry rheology whereby the compressive and bending strengths of the ceramic foam filter is substantially increased as compared with alumina-chromia filter elements. 
     
     
       2. A filter according to claim 1 containing from 2.5 to 25% of an air setting agent which is substantially nonreactive to the molten metal. 
     
     
       3. A filter according to claim 2 wherein said air setting agent is aluminum orthophosphate. 
     
     
       4. A filter according to claim 3 containing from 15 to 25% aluminum orthophosphate. 
     
     
       5. A filter according to claim 1 containing from 60 to 65% Al 2  O 3 . 
     
     
       6. A filter according to claim 1 containing from 2 to 5% micron-sized reactive alumina. 
     
     
       7. A filter according to claim 1 containing from 1 to 3% ceramic fibers. 
     
     
       8. A filter according to claim 7 wherein said ceramic fibers are alumina-silicate fibers.